The present invention relates to the construction of nuclear reactors in which the fuel elements constituting the core are cooled by the flow of a cooling liquid through the core, along individual elements arranged parallel to one another. It relates more particularly to means which permit partitioning of the core and thereby organization of the flow of cooling liquid or refrigerant, in order to avoid the appearance of preferential paths, detrimental to the efficiency, although the cross-section offered to the flow is not generally uniformly occupied by the fuel elements.
Thus in particular, in liquid cooled reactors, the fuel is in the form of rods grouped in assemblies traversed by the refrigerant fluid. The core is constituted by such juxtaposed assemblies, stowed close to one another, each assembly being prismatic, generally with a square cross-section. The periphery of the core then necessarily presents steps. The assembly is arranged in an enveloping skirt supporting the cores, which is, itself of cylindrical shape, or at least without corners, like the tank which contains the core and its appended equipment, bathed in the cooling liquid. Thus, between the peripheral assemblies and the enveloping skirt, there is an annular zone which is devoid of fuel.